U.S. patent number 9,906,196 [Application Number 15/270,631] was granted by the patent office on 2018-02-27 for hybrid switched mode amplifier.
This patent grant is currently assigned to Cirrus Logic, Inc.. The grantee listed for this patent is Cirrus Logic International Semiconductor Ltd.. Invention is credited to Zhaohui He, Eric J. King, Siddharth Maru, John L. Melanson.
United States Patent |
9,906,196 |
He , et al. |
February 27, 2018 |
Hybrid switched mode amplifier
Abstract
A switching power stage for producing a load voltage may include
a first processing path having a first output, a second processing
path having a second output, a first plurality of switches
comprising at least a first switch coupled between the first output
and a first load terminal and a second switch coupled between the
first output and the second load terminal, a second plurality of
switches comprising at least a third switch coupled between the
second output and the first load terminal and a fourth switch
coupled between the second output and the second load terminal, and
a controller configured to control switches in order to generate
the load voltage as a function of an input signal such that one of
the first switch and the second switch operates in a linear region
of operation and one of the third switch and the fourth switch
operates in a saturated region of operation for a predominance of a
dynamic rage of the load voltage.
Inventors: |
He; Zhaohui (Austin, TX),
King; Eric J. (Dripping Springs, TX), Maru; Siddharth
(Austin, TX), Melanson; John L. (Austin, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Cirrus Logic International Semiconductor Ltd. |
Edinburgh |
N/A |
GB |
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Assignee: |
Cirrus Logic, Inc. (Austin,
TX)
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Family
ID: |
59314946 |
Appl.
No.: |
15/270,631 |
Filed: |
September 20, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170207759 A1 |
Jul 20, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15168680 |
May 31, 2016 |
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62279956 |
Jan 18, 2016 |
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62309068 |
Mar 16, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03F
3/45475 (20130101); H03F 3/217 (20130101); H03F
3/185 (20130101); H03F 3/2173 (20130101); H03F
1/04 (20130101); H03F 1/34 (20130101); H03F
2200/351 (20130101); H04R 3/12 (20130101); H04R
2420/03 (20130101); H03F 2203/45034 (20130101); H03F
2200/432 (20130101); H03F 3/2171 (20130101) |
Current International
Class: |
H03F
3/217 (20060101); H03F 3/185 (20060101); H03F
3/45 (20060101); H03F 1/04 (20060101); H03F
1/34 (20060101); H04R 3/12 (20060101) |
Field of
Search: |
;330/251,207A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1367704 |
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Dec 2003 |
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EP |
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2510395 |
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Aug 2014 |
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GB |
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2546576 |
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Jul 2017 |
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GB |
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S59224905 |
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Dec 1984 |
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JP |
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98/57422 |
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Dec 1998 |
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WO |
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2007136800 |
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Nov 2007 |
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WO |
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2017127132 |
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Jul 2017 |
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WO |
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2017127353 |
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Jul 2017 |
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WO |
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Other References
International Search Report and Written Opinion of the
International Searching Authority, International Patent Application
No. PCT/US2016/040072, dated Sep. 16, 2016, 10 pages. cited by
applicant .
Combined Search and Examination Report under Sections 17 and 18(3)
of the UKIPO, Application No. GB1701269.1, dated Jul. 7, 2017.
cited by applicant .
Combined Search and Examination Report under Sections 17 and 18(3)
of the UKIPO, Application No. GB1703492.7, dated Aug. 31, 2017.
cited by applicant .
Combined Search and Examination Report under Sections 17 and 18(3)
of the UKIPO, Application No. GB1703865.4, dated Aug. 31, 2017.
cited by applicant .
Combined Search Report and Written Opinion, GB Application No.
1617096.1, dated Apr. 7, 2017. cited by applicant .
Search Report, GB Application No. 1619679.2, dated Apr. 28, 2017.
cited by applicant .
International Search Report and Written Opinion of the
International Searching Authority, International Patent Application
No. PCT/US2017/020927, dated May 26, 2017. cited by applicant .
International Search Report and Written Opinion of the
International Searching Authority, International Patent Application
No. PCT/US2017/021351, dated May 26, 2017. cited by applicant .
International Search Report and Written Opinion of the
International Searching Authority, International Patent Application
No. PCT/US2017/013756, dated May 30, 2017. cited by applicant .
International Search Report and Written Opinion of the
International Searching Authority, International Application No.
PCT/US2017/020911, dated Nov. 7, 2017. cited by applicant.
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Primary Examiner: Nguyen; Khanh V
Attorney, Agent or Firm: Jackson Walker L.L.P.
Parent Case Text
RELATED APPLICATIONS
The present disclosure claims priority to U.S. Provisional Patent
Application Ser. No. 62/309,068, filed Mar. 16, 2016, and is a
continuation-in-part of U.S. patent application Ser. No.
15/168,680, filed May 31, 2016, which claims priority to U.S.
Provisional Patent Application Ser. No. 62/279,956, filed Jan. 18,
2016, and both of which are incorporated by reference herein in
their entirety.
Claims
What is claimed is:
1. A switching power stage for producing a load voltage at a load
output of the switching power stage, the load output comprising a
first load terminal having a first load voltage and a second load
terminal having a second load voltage such that the load voltage
comprises a difference between the first load voltage and the
second load voltage, the switching power stage comprising: a power
converter comprising a power inductor and a first plurality of
switches, wherein the power converter is configured to drive a
power converter output terminal coupled to the first load terminal
in order to drive the first load terminal; a linear amplifier
configured to drive a linear amplifier output terminal coupled to
the second load terminal in order to drive the second load
terminal; a second plurality of switches, comprising at least a
first switch coupled between the power converter output terminal
and the first load terminal and a second switch coupled between the
power converter output terminal and the second load terminal such
that the power converter output terminal and the first load
terminal are coupled via the first switch and the power converter
output terminal and the second load terminal are coupled via the
second switch; a third plurality of switches, comprising at least a
third switch coupled between the linear amplifier output terminal
and the first load terminal and a fourth switch coupled between the
linear amplifier output terminal and the second load terminal such
that the linear amplifier output terminal and the first load
terminal are coupled via the third switch and the linear amplifier
output terminal and the second load terminal are coupled via the
fourth switch; and a controller configured to control the first
plurality of switches, the second plurality of switches, the third
plurality of switches, and the linear amplifier in order to
generate the load voltage as a function of an input signal to the
controller such that energy delivered to the load output is
supplied predominantly by the power converter, and such that one of
the first switch and the second switch operates in a linear region
of operation and one of the third switch and the fourth switch
operates in a saturated region of operation for a predominance of a
dynamic range of the load voltage.
2. The switching power stage of claim 1, further comprising a
capacitor coupled between the first load terminal and the second
load terminal.
3. The switching power stage of claim 1, further comprising a
capacitor coupled between the first load terminal and one of a
first supply terminal having a first voltage and a second supply
terminal having a second voltage.
4. The switching power stage of claim 3, wherein a second terminal
of the power inductor is coupled to the power converter output
terminal.
5. The switching power stage of claim 3, wherein the first
plurality of switches comprises: a first switch coupled between a
second terminal of the power inductor and the power converter
output terminal; and a second switch coupled between the second
terminal of the power inductor and the second supply terminal.
6. The switching power stage of claim 1, further comprising: a
first capacitor coupled between the power converter output terminal
and one of a first supply terminal having a first voltage and a
second supply terminal having a second voltage; and a second
capacitor coupled between the second load terminal and one of the
first supply terminal and the second supply terminal.
7. The switching power stage of claim 1, wherein the first
plurality of switches comprises: a fifth switch coupled between a
first terminal of the power inductor and a first supply terminal
having a first voltage; and a sixth switch coupled between the
first terminal of the power inductor and a second supply terminal
having a second voltage.
8. The switching power stage of claim 7, wherein the first
plurality of switches further comprises: a seventh switch coupled
between a second terminal of the power inductor and the power
converter output terminal; and an eighth switch coupled between the
second terminal of the power inductor and the second supply
terminal.
9. The switching power stage of claim 1, wherein the controller
further controls the first plurality of switches to drive the first
load voltage as a function of a target output voltage which is a
function of the input signal.
10. The switching power stage of claim 9, wherein the function of
the target output voltage includes a magnitude of the target output
voltage.
11. The switching power stage of claim 9, wherein the function of
the target output voltage includes a lower saturation limit of the
power converter output terminal.
12. The switching power stage of claim 11, wherein the controller
further controls the linear amplifier to drive a non-zero voltage
as the second load voltage in order to increase a common mode
voltage of the first load terminal and the second load terminal
when the power converter output terminal is driven to the lower
saturation limit in order to produce the output voltage as a
function of an input signal to the controller while minimizing
non-linearities of the output voltage as a function of the input
signal.
13. The switching power stage of claim 1, wherein the controller
further controls the linear amplifier to drive the second load
voltage as a function of a target output voltage which is a
function of the input signal.
14. A method for producing a load voltage at a load output of the
switching power stage, the load output comprising a first load
terminal having a first load voltage and a second load terminal
having a second load voltage such that the load voltage comprises a
difference between the first load voltage and the second load
voltage, wherein the switching power stage comprises: a power
converter comprising a power inductor and a first plurality of
switches, wherein the power converter is configured to drive a
power converter output terminal coupled to the first load terminal
in order to drive the first load terminal; a linear amplifier
configured to drive a linear amplifier output terminal coupled to
the second load terminal in order to drive the second load
terminal; a second plurality of switches, comprising at least a
first switch coupled between the power converter output terminal
and the first load terminal and a second switch coupled between the
power converter output terminal and the second load terminal such
that the power converter output terminal and the first load
terminal are coupled via the first switch and the power converter
output terminal and the second load terminal are coupled via the
second switch; and a third plurality of switches, comprising at
least a third switch coupled between the linear amplifier output
terminal and the first load terminal and a fourth switch coupled
between the linear amplifier output terminal and the second load
terminal such that the linear amplifier output terminal and the
first load terminal are coupled via the third switch and the linear
amplifier output terminal and the second load terminal are coupled
via the fourth switch; wherein the method comprises controlling the
first plurality of switches, the second plurality of switches, the
third plurality of switches, and the linear amplifier in order to
generate the load voltage as a function of an input signal to the
controller such that energy delivered to the load output is
supplied predominantly by the power converter, and such that one of
the first switch and the second switch operates in a linear region
of operation and one of the third switch and the fourth switch
operates in a saturated region of operation for a predominance of a
dynamic range of the load voltage.
15. The method of claim 14, further comprising a capacitor coupled
between the first load terminal and the second load terminal.
16. The method of claim 14, further comprising a capacitor coupled
between the first load terminal and one of a first supply terminal
having a first voltage and a second supply terminal having a second
voltage.
17. The method of claim 16, wherein a second terminal of the power
inductor is coupled to the power converter output terminal.
18. The method of claim 16, wherein the first plurality of switches
comprises: a first switch coupled between a second terminal of the
power inductor and the power converter output terminal; and a
second switch coupled between the second terminal of the power
inductor and the second supply terminal.
19. The method of claim 14, further comprising: a first capacitor
coupled between the power converter output terminal and one of a
first supply terminal having a first voltage and a second supply
terminal having a second voltage; and a second capacitor coupled
between the second load terminal and one of the first supply
terminal and the second supply terminal.
20. The method of claim 14, wherein the first plurality of switches
comprises: a fifth switch coupled between a first terminal of the
power inductor and a first supply terminal having a first voltage;
and a sixth switch coupled between the first terminal of the power
inductor and a second supply terminal having a second voltage.
21. The method of claim 20, wherein the first plurality of switches
further comprises: a seventh switch coupled between a second
terminal of the power inductor and the power converter output
terminal; and an eighth switch coupled between the second terminal
of the power inductor and the second supply terminal.
22. The method of claim 14, wherein the controller further controls
the first plurality of switches to drive the first load voltage as
a function of a target output voltage which is a function of the
input signal.
23. The method of claim 22, wherein the function of the target
output voltage includes a magnitude of the target output
voltage.
24. The method of claim 23, wherein the function of the target
output voltage includes a lower saturation limit of the power
converter output terminal.
25. The method of claim 24, wherein the controller further controls
the linear amplifier to drive a non-zero voltage as the second load
voltage in order to increase a common mode voltage of the first
load terminal and the second load terminal when the power converter
output terminal is driven to the lower saturation limit in order to
produce the output voltage as a function of an input signal to the
controller while minimizing non-linearities of the output voltage
as a function of the input signal.
26. The method of claim 14, wherein the controller further controls
the linear amplifier to drive the second load voltage as a function
of a target output voltage which is a function of the input
signal.
27. A switching power stage for producing a load voltage at a load
output of the switching power stage, the load output comprising a
first load terminal having a first load voltage and a second load
terminal having a second load voltage such that the load voltage
comprises a difference between the first load voltage and the
second load voltage, the switching power stage comprising: a first
processing path configured to process a first signal derived from
an input signal to generate a first path voltage at a first
processing path output; a second processing path configured to
process a second signal derived from the input signal to generate a
second path voltage at a second processing path output; a first
plurality of switches, comprising at least a first switch coupled
between the first processing path output and the first load
terminal and a second switch coupled between the first processing
path output and the second load terminal; a second plurality of
switches, comprising at least a third switch coupled between the
second processing path output and the first load terminal and a
fourth switch coupled between the second processing path output and
the second load terminal; and a controller configured to control
the first plurality of switches and the second plurality of
switches in order to generate the load voltage as a function of the
input signal such that one of the first switch and the second
switch operates in a linear region of operation and one of the
third switch and the fourth switch operates in a saturated region
of operation for a predominance of a dynamic range of the load
voltage.
28. A method for producing a load voltage at a load output of a
switching power stage, the load output comprising a first load
terminal having a first load voltage and a second load terminal
having a second load voltage such that the load voltage comprises a
difference between the first load voltage and the second load
voltage, wherein the switching power stage comprises a first
processing path configured to process a first signal derived from
an input signal to generate a first path voltage at a first
processing path output, a second processing path configured to
process a second signal derived from the input signal to generate a
second path voltage at a second processing path output, a first
plurality of switches, comprising at least a first switch coupled
between the first processing path output and the first load
terminal and a second switch coupled between the first processing
path output and the second load terminal, and a second plurality of
switches, comprising at least a third switch coupled between the
second processing path output and the first load terminal and a
fourth switch coupled between the second processing path output and
the second load terminal, the method comprising: controlling the
first plurality of switches and the second plurality of switches in
order to generate the load voltage as a function of the input
signal such that one of the first switch and the second switch
operates in a linear region of operation and one of the third
switch and the fourth switch operates in a saturated region of
operation for a predominance of a dynamic range of the load
voltage.
Description
FIELD OF DISCLOSURE
The present disclosure relates in general to circuits for audio
devices, including without limitation personal audio devices such
as wireless telephones and media players, and more specifically, to
a switched mode amplifier including a switched mode converter for
driving an audio transducer of an audio device.
BACKGROUND
Personal audio devices, including wireless telephones, such as
mobile/cellular telephones, cordless telephones, mp3 players, and
other consumer audio devices, are in widespread use. Such personal
audio devices may include circuitry for driving a pair of
headphones or one or more speakers. Such circuitry often includes a
speaker driver including a power amplifier for driving an audio
output signal to headphones or speakers.
SUMMARY
In accordance with the teachings of the present disclosure, one or
more disadvantages and problems associated with existing approaches
to driving an audio output signal to an audio transducer may be
reduced or eliminated.
In accordance with embodiments of the present disclosure, a
switching power stage for producing a load voltage at a load output
of the switching power stage, wherein the load output comprising a
first load terminal having a first load voltage and a second load
terminal having a second load voltage such that the load voltage
comprises a difference between the first load voltage and the
second load voltage, may include a power converter comprising a
power inductor and a first plurality of switches, wherein the power
converter is configured to drive a power converter output terminal
coupled to the first load terminal in order to drive the first load
terminal, a linear amplifier configured to drive a linear amplifier
output terminal coupled to the second load terminal in order to
drive the second load terminal, a second plurality of switches
comprising at least a first switch coupled between the power
converter output terminal and the first load terminal and a second
switch coupled between the power converter output terminal and the
second load terminal such that the power converter output terminal
and the first load terminal are coupled via the first switch and
the power converter output terminal and the second load terminal
are coupled via the second switch, and a third plurality of
switches comprising at least a third switch coupled between the
linear amplifier output terminal and the first load terminal and a
fourth switch coupled between the linear amplifier output terminal
and the second load terminal such that the linear amplifier output
terminal and the first load terminal are coupled via the third
switch and the linear amplifier output terminal and the second load
terminal are coupled via the fourth switch. The switching power
stage may also comprise a controller configured to control the
first plurality of switches, the second plurality of switches, the
third plurality of switches, and the linear amplifier in order to
generate the load voltage as a function of an input signal to the
controller such that energy delivered to the load output is
supplied predominantly by the power converter, and such that one of
the first switch and the second switch operates in a linear region
of operation and one of the third switch and the fourth switch
operates in a saturated region of operation for a predominance of a
dynamic range of the load voltage.
In accordance with these and other embodiments of the present
disclosure, a method may be provided for producing a load voltage
at a load output of the switching power stage, the load output
comprising a first load terminal having a first load voltage and a
second load terminal having a second load voltage such that the
load voltage comprises a difference between the first load voltage
and the second load voltage, wherein the switching power stage
comprises a power converter comprising a power inductor and a first
plurality of switches, wherein the power converter is configured to
drive a power converter output terminal coupled to the first load
terminal in order to drive the first load terminal, a linear
amplifier configured to drive a linear amplifier output terminal
coupled to the second load terminal in order to drive the second
load terminal, a second plurality of switches comprising at least a
first switch coupled between the power converter output terminal
and the first load terminal and a second switch coupled between the
power converter output terminal and the second load terminal such
that the power converter output terminal and the first load
terminal are coupled via the first switch and the power converter
output terminal and the second load terminal are coupled via the
second switch, and a third plurality of switches comprising at
least a third switch coupled between the linear amplifier output
terminal and the first load terminal and a fourth switch coupled
between the linear amplifier output terminal and the second load
terminal such that the linear amplifier output terminal and the
first load terminal are coupled via the third switch and the linear
amplifier output terminal and the second load terminal are coupled
via the fourth switch. The method may include controlling the first
plurality of switches, the second plurality of switches, the third
plurality of switches, and the linear amplifier in order to
generate the load voltage as a function of an input signal to the
controller such that energy delivered to the load output is
supplied predominantly by the power converter, and such that one of
the first switch and the second switch operates in a linear region
of operation and one of the third switch and the fourth switch
operates in a saturated region of operation for a predominance of a
dynamic range of the load voltage.
In accordance with these and other embodiments of the present
disclosure, a switching power stage for producing a load voltage at
a load output of the switching power stage, wherein the load output
comprises a first load terminal having a first load voltage and a
second load terminal having a second load voltage such that the
load voltage comprises a difference between the first load voltage
and the second load voltage, may include a first processing path
configured to process a first signal derived from an input signal
to generate a first path voltage at a first processing path output,
a second processing path configured to process a second signal
derived from the input signal to generate a second path voltage at
a second processing path output, a first plurality of switches
comprising at least a first switch coupled between the first
processing path output and the first load terminal and a second
switch coupled between the first processing path output and the
second load terminal, a second plurality of switches comprising at
least a third switch coupled between the second processing path
output and the first load terminal and a fourth switch coupled
between the second processing path output and the second load
terminal, and a controller configured to control the first
plurality of switches and the second plurality of switches in order
to generate the load voltage as a function of the input signal such
that one of the first switch and the second switch operates in a
linear region of operation and one of the third switch and the
fourth switch operates in a saturated region of operation for a
predominance of a dynamic range of the load voltage.
In accordance with these and other embodiments of the present
disclosure, a method may be provided for producing a load voltage
at a load output of a switching power stage, the load output
comprising a first load terminal having a first load voltage and a
second load terminal having a second load voltage such that the
load voltage comprises a difference between the first load voltage
and the second load voltage, wherein the switching power stage
comprises a first processing path configured to process a first
signal derived from an input signal to generate a first path
voltage at a first processing path output, a second processing path
configured to process a second signal derived from the input signal
to generate a second path voltage at a second processing path
output, a first plurality of switches comprising at least a first
switch coupled between the first processing path output and the
first load terminal and a second switch coupled between the first
processing path output and the second load terminal, and a second
plurality of switches comprising at least a third switch coupled
between the second processing path output and the first load
terminal and a fourth switch coupled between the second processing
path output and the second load terminal. The method may include
controlling the first plurality of switches and the second
plurality of switches in order to generate the load voltage as a
function of the input signal such that one of the first switch and
the second switch operates in a linear region of operation and one
of the third switch and the fourth switch operates in a saturated
region of operation for a predominance of a dynamic range of the
load voltage.
Technical advantages of the present disclosure may be readily
apparent to one skilled in the art from the figures, description
and claims included herein. The objects and advantages of the
embodiments will be realized and achieved at least by the elements,
features, and combinations particularly pointed out in the
claims.
It is to be understood that both the foregoing general description
and the following detailed description are examples and explanatory
and are not restrictive of the claims set forth in this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
FIG. 1 illustrates an example personal audio device, in accordance
with embodiments of the present disclosure;
FIG. 2 illustrates a block diagram of selected components of an
example audio integrated circuit of a personal audio device, in
accordance with embodiments of the present disclosure;
FIG. 3 illustrates a block and circuit diagram of selected
components of an example switched mode amplifier, in accordance
with embodiments of the present disclosure;
FIG. 4 illustrates a circuit diagram of selected components of an
example boost converter that may be used to implement the power
converter depicted in FIG. 3, in accordance with embodiments of the
present disclosure;
FIG. 5 illustrates a circuit diagram of selected components of an
example output stage that may be used to implement the output stage
depicted in FIG. 3, in accordance with embodiments of the present
disclosure;
FIG. 6 illustrates a graph depicting the relationship of a voltage
driven by the power converter depicted in FIG. 3 and a voltage
driven by a linear amplifier of the output stage depicted in FIG. 3
as a function of a desired output voltage, in accordance with
embodiments of the present disclosure;
FIG. 7 illustrates a circuit diagram of selected components of an
example linear amplifier that may be used to implement the linear
amplifier depicted in FIG. 5, in accordance with embodiments of the
present disclosure;
FIG. 8 illustrates a circuit diagram of selected components of
another example output stage that may be used to implement the
second control loop depicted in FIG. 3, in accordance with
embodiments of the present disclosure; and
FIG. 9 illustrates a circuit diagram of selected components of an
example linear amplifier that may be used to implement the linear
amplifier depicted in FIG. 8, in accordance with embodiments of the
present disclosure.
DETAILED DESCRIPTION
FIG. 1 illustrates an example personal audio device 1, in
accordance with embodiments of the present disclosure. FIG. 1
depicts personal audio device 1 coupled to a headset 3 in the form
of a pair of earbud speakers 8A and 8B. Headset 3 depicted in FIG.
1 is merely an example, and it is understood that personal audio
device 1 may be used in connection with a variety of audio
transducers, including without limitation, headphones, earbuds,
in-ear earphones, and external speakers. A plug 4 may provide for
connection of headset 3 to an electrical terminal of personal audio
device 1. Personal audio device 1 may provide a display to a user
and receive user input using a touch screen 2, or alternatively, a
standard liquid crystal display (LCD) may be combined with various
buttons, sliders, and/or dials disposed on the face and/or sides of
personal audio device 1. As also shown in FIG. 1, personal audio
device 1 may include an audio integrated circuit (IC) 9 for
generating an analog audio signal for transmission to headset 3
and/or another audio transducer.
FIG. 2 illustrates a block diagram of selected components of an
example audio IC 9 of a personal audio device, in accordance with
embodiments of the present disclosure. As shown in FIG. 2, a
microcontroller core 18 may supply a digital audio input signal
DIG_IN to a digital-to-analog converter (DAC) 14, which may convert
the digital audio input signal to an analog signal V.sub.IN. DAC 14
may supply analog signal V.sub.IN to an amplifier 16 which may
amplify or attenuate audio input signal V.sub.IN to provide a
differential audio output signal V.sub.OUT, which may operate a
speaker, a headphone transducer, a line level signal output, and/or
other suitable output. In some embodiments, DAC 14 may be an
integral component of amplifier 16. A power supply 10 may provide
the power supply rail inputs of amplifier 16. In some embodiments,
power supply 10 may comprise a battery. Although FIGS. 1 and 2
contemplate that audio IC 9 resides in a personal audio device,
systems and methods described herein may also be applied to
electrical and electronic systems and devices other than a personal
audio device, including audio systems for use in a computing device
larger than a personal audio device, an automobile, a building, or
other structure.
FIG. 3 illustrates a block and circuit diagram of selected
components of an example switched mode amplifier 20, in accordance
with embodiments of the present disclosure. In some embodiments,
switched mode amplifier 20 may implement all or a portion of
amplifier 16 described with respect to FIG. 2. As shown in FIG. 3,
switched mode amplifier 20 may comprise a loop filter 22, a
controller 24, a power converter 26, and an second control loop
28.
Loop filter 22 may comprise any system, device, or apparatus
configured to receive an input signal (e.g., audio input signal
V.sub.IN or a derivative thereof) and a feedback signal (e.g.,
audio output signal V.sub.OUT, a derivative thereof, or other
signal indicative of audio output signal V.sub.OUT) and based on
such input signal and feedback signal, generate a controller input
signal to be communicated to controller 24. In some embodiments,
such controller input signal may comprise a signal indicative of an
integrated error between the input signal and the feedback signal.
In other embodiments, such controller input signal may comprise a
signal indicative of a target current signal to be driven as an
output current I.sub.OUT or a target voltage signal to be driven as
an output voltage V.sub.OUT to a load coupled to the output
terminals of second control loop 28.
Controller 24 may comprise any system, device, or apparatus
configured to, based on an input signal (e.g., input signal INPUT),
output signal V.sub.OUT, and/or other characteristics of switched
mode amplifier 20, control switching of switches integral to power
converter 26, switches integral to second control loop 28, and/or
one or more linear amplifiers integral to second control loop 28,
in order to transfer electrical energy from a power supply
V.sub.SUPPLY to the load of switched-mode amplifier 20 in
accordance with the input signal.
Power converter 26 may receive at its input a voltage V.sub.SUPPLY
(e.g., provided by power supply 10), and may generate at its output
a voltage V.sub.PC. In some embodiments, voltage V.sub.SUPPLY may
be received via input terminals including a positive input terminal
and a negative input terminal which may be coupled to a ground
voltage. As described in greater detail in this disclosure
(including, without limitation, in reference to FIG. 4, below),
power converter 26 may comprise a power inductor and a plurality of
switches that are controlled by control signals received from
controller 24 in order to convert voltage V.sub.SUPPLY to voltage
V.sub.PC, such that audio output signal V.sub.OUT generated from
voltage V.sub.PC is a function of the input signal to loop filter
22. Also as shown in FIG. 3, a capacitor 27 may be coupled between
a second supply terminal (which may in some embodiments be coupled
to ground) and the power converter output terminal. However, in
other embodiments, capacitor 27 may be coupled between a first
supply terminal and the power converter output terminal.
Turning briefly to FIG. 4, a non-limiting example of a single-ended
switching mode power supply which may be used to implement power
converter 26 is described. FIG. 4 illustrates a circuit diagram of
selected components of an example buck converter 40 that may be
used to implement power converter 26 depicted in FIG. 3, in
accordance with embodiments of the present disclosure. As shown in
FIG. 4, buck converter 40 may include a power inductor 42, switches
44, 46, 47, and 49 and capacitor 27 arranged as shown. In
operation, controller 24 may be configured to, when non-inverting
buck-boost converter 40 is used to implement power converter 26,
control switches 44, 46, 47, and 49 such that power converter
output voltage V.sub.PC is a function of the controller input
signal provided to controller 24.
Turning again to FIG. 3, second control loop 28 may receive at its
input the power converter output voltage V.sub.PC, and may generate
at its output audio output signal V.sub.OUT. As described in
greater detail in this disclosure (including, without limitation,
in reference to FIGS. 5A and 5B, below), second control loop 28 may
comprise at least one linear amplifier and, in some embodiments, a
plurality of switches, wherein the at least one linear amplifier
and the plurality of switches, if present, are controlled by
control signals received from controller 24 in order to convert
power converter output voltage V.sub.PC to audio output signal
V.sub.OUT, such that audio output signal V.sub.OUT is a function of
the input signal to loop filter 22.
FIG. 5 illustrates a circuit diagram of selected components of an
example output stage 28A that may be used to implement second
control loop 28 depicted in FIG. 3, in accordance with embodiments
of the present disclosure. As shown in FIG. 5, power converter 26
may drive power converter output voltage V.sub.PC. Output stage 28A
may comprise a plurality of switches including switch 64 coupled
between the power converter output and a first output terminal of
output stage 28A and switch 66 coupled between the power converter
output and a second output terminal of output stage 28A. In
addition, second control loop 28 may include a linear amplifier 60
(an example of which is depicted in FIG. 7) configured to drive a
linear amplifier output voltage V.sub.AMP. Output stage 28A may
also include a plurality of switches including switch 68 coupled
between the output of linear amplifier 60 and a first output
terminal of output stage 28A and switch 70 coupled between the
output of linear amplifier 60 and a second output terminal of
output stage 28A.
In operation of output stage 28A, controller 24 may activate
switches 64 and 70 and deactivate switches 66 and 68 for positive
values of audio output signal V.sub.OUT and activate switches 66
and 68 and deactivate switches 64 and 70 for negative values of
audio output signal V.sub.OUT. Controller 24 may, as power
converter output voltage V.sub.PC approaches the lower saturation
limit, cause linear amplifier 60 to drive a non-zero linear
amplifier output voltage V.sub.AMP in order to increase a common
mode voltage between the first output terminal and the second
output terminal, allowing audio output signal V.sub.OUT to approach
and cross zero. Above the lower saturation limit of power converter
output voltage V.sub.PC, controller 24 may cause linear amplifier
60 to drive an approximately zero linear amplifier output voltage
V.sub.AMP such that a magnitude of audio output signal V.sub.OUT is
equal to power converter output voltage V.sub.PC.
In other words, controller 24 may control power converter 26 and
linear amplifier 60 to generate voltages in accordance with the
following functions, which are graphically depicted in FIG. 6, and
wherein voltage V.sub.TGT represents a target or desired voltage to
be output as audio output signal V.sub.OUT as indicated by the
input signal to controller 24: V.sub.PC=V.sub.TGT;for
|V.sub.TGT|>V.sub.SAT V.sub.PC=V.sub.SAT;for
|V.sub.TGT|.ltoreq.V.sub.SAT V.sub.AMP=0;for
|V.sub.TGT|>V.sub.SAT V.sub.AMP=V.sub.SAT-V.sub.TGT;for
|V.sub.TGT|.ltoreq.V.sub.SAT
In some embodiments, an offset voltage may be added to each of the
output of power converter 26 and the output of linear amplifier 60,
to ensure that the voltage V.sub.AMP>0 at all times.
Accordingly, presence of linear amplifier 60 and its ability to
increase the common mode voltage of the output terminals in
response to low magnitudes of the output signal V.sub.OUT may
minimize non-linearities of output signal V.sub.OUT as a function
of the input signal received by controller 24, and permit crossing
a magnitude of zero by audio output signal V.sub.OUT.
FIG. 7 illustrates a circuit diagram of selected components of an
example linear amplifier 71A that may be used to implement linear
amplifier 60 depicted in FIG. 5, in accordance with embodiments of
the present disclosure. As shown in FIG. 7, linear amplifier 71A
may include a first stage 74 and a second stage 76. First stage 74
may comprise a gain stage 78 having a transconductance gain Gm to
convert a voltage signal INPUT received from controller 24 to a
current I.sub.E.
Second stage 76 may comprise a totem-pole topology with an input at
a gate terminal of n-type field effect transistor (NFET) 80 and an
output node shared by the drain terminal of NFET 82 of source
terminal of NFET 80 at which linear amplifier 71A drives linear
amplifier output voltage V.sub.AMP. In such topology, NFET 80 may
source current into a load coupled to the output node and NFET 82
may sink current from such load. A local current feedback loop may
be arranged with respect to NFET 82 in order to regulate a minimum
level of quiescent current through NFET 80. Thus, second stage 76
may be viewed as a source follower having a unity gain from its
input node (e.g. gate terminal of NFET 80) to its output node.
Within the current feedback loop of second stage 76, a
current-sensing amplifier 84 may sense a current associated with
NFET 80 generating a scaled current to be compared with a reference
current I.sub.REF, resulting in an error current equal to the
difference between the scaled current and reference current
I.sub.REF. A gain booster stage 86 may receive the error current
and operate as a current mirror to compensate for loss of loop gain
due to the current sensing scheme of current-sensing amplifier 84.
At the output of gain booster stage 86, a conventional
Miller-compensated common-source output scheme may be applied for
stability as long as NFET 82 remains in its saturation region,
which may be maintained by keeping its drain-to-source voltage
V.sub.DS being greater than a saturation voltage
V.sub.d.sub._.sub.sat. For example, when drain-to-source voltage
V.sub.ds becomes less than V.sub.d.sub._.sub.sat for a given
drain-to-source voltage I.sub.ds of NFET 82, an output drain
impendance of NFET 82 may decrease, and a voltage gain of NFET 82
will decrease accordingly. Consequently, the current loop gain and
unity-gain bandwidth of the local current feedback loop may
decrease. When such an amplifier is integral to a high-order
feedback loop, reduction of unity-gain bandwidth may lead to system
instability and must be avoided. Therefore, gain-compensator 88 may
be present and may include a variable current gain as a function of
drain-to-source voltage of NFET 82, which in the first order can be
translated to an output impedance of NFET 82.
FIG. 8 illustrates a circuit diagram of selected components of
another example output stage 28B that may be used to implement
second control loop 28 depicted in FIG. 3, in accordance with
embodiments of the present disclosure. Output stage 28B of FIG. 8
may be similar in many respects to output stage 28A of FIG. 5, and
thus, only the main differences between output stage 28B and output
stage 28A are discussed in detail. One main difference between
output stage 28B and output stage 28A is that in output stage 28B,
linear amplifier 60, switch 64, switch 66, switch 68, and/or switch
70 may be integral to a final output stage of a differential
amplifier 72.
To further illustrate, FIG. 9 illustrates a circuit diagram of an
example linear amplifier 71B which may be used to implement
portions of the example output stage 28B depicted in FIG. 8, in
accordance with embodiments of the present disclosure. As one of
skill in the relevant art may recognize, linear amplifier 71B may
comprise the differential-output analog to the single-ended
topology of linear amplifier 71A depicted in FIG. 7, and analogous
components of linear amplifier 71B have the same reference numerals
as that of linear amplifier 71A with an additional letter "A" or
"B" added to the reference numerals. In some embodiments, one or
more of NFETs 80A, 80B, 82A, and 82B may be equivalent to switches
64, 66, 68, and 70, respectively, of output stage 28B of FIG.
8.
In these and other embodiments, additional circuitry may be present
to cause the gate-to-source voltage of switch 66 and/or 64 to be at
or greater than supply voltage(s) in order to operate as a switch
(e.g., activate and deactivate). In these and other embodiments,
switch 70 and/or 68 may operate in the linear region of such
devices, wherein the gate-to-source voltage of such devices is less
than the supply voltage.
In light of the foregoing, in operation, switches 68 and 70 of
example output stage 28B may be viewed as ground-referenced devices
in a first differential amplifier and switches 64 and 66 may be
viewed as supply voltage-referenced devices of a second
differential amplifier example output stage 28B. When viewed in
such manner, the behavior of the amplifier described herein
operates to control polarity and magnitude of output voltage
V.sub.OUT by operating such first and second differential
amplifiers such that, when implemented as transistors (e.g., n-type
metal-oxide-semiconductor field-effect transistors), one switch in
each of the differential amplifiers may operate in its saturation
region while the remaining switch in each of the differential
amplifiers may operate in its linear region. For example, when
switch 64 operates in its saturated region, switch 66 may operate
in its linear region, and vice versa. When switch 68 operates in
its saturated region, switch 70 may operate in its linear region,
and vice versa. Because of this behavior, non-idealities (such as
high-frequency switching ripple) may be divided between such
differential amplifiers such that the predominance of ripple is
seen by one switch in each such differential amplifier.
In the foregoing discussion, embodiments are disclosed in which a
capacitor 27 is coupled between the power converter output terminal
and one of a first supply terminal having a first voltage and a
second supply terminal having a second voltage, and embodiments are
disclosed in which a capacitor 62 is coupled between the first load
terminal and the second load terminal of switched mode amplifier
20. However, in these and other embodiments, a capacitor may be
coupled between the first load terminal of switched mode amplifier
20 and one of the first supply terminal and the second supply
terminal. In addition, in these and other embodiments, a capacitor
may be coupled between the second load terminal of switched mode
amplifier 20 and one of the first supply terminal and the second
supply terminal.
As used herein, a "switch" may comprise any suitable device,
system, or apparatus for making a connection in an electric circuit
when the switch is enabled (e.g., activated, closed, or on) and
breaking the connection when the switch is disabled (e.g.,
deactivated, open, or off) in response to a control signal received
by the switch. For purposes of clarity and exposition, control
signals for switches described herein are not depicted although
such control signals would be present to selectively enable and
disable such switches. In some embodiments, a switch may comprise a
metal-oxide-semiconductor field-effect transistor (e.g., an n-type
metal-oxide-semiconductor field-effect transistor).
As used herein, when two or more elements are referred to as
"coupled" to one another, such term indicates that such two or more
elements are in electronic communication or mechanical
communication, as applicable, whether connected indirectly or
directly, with or without intervening elements.
This disclosure encompasses all changes, substitutions, variations,
alterations, and modifications to the exemplary embodiments herein
that a person having ordinary skill in the art would comprehend.
Similarly, where appropriate, the appended claims encompass all
changes, substitutions, variations, alterations, and modifications
to the exemplary embodiments herein that a person having ordinary
skill in the art would comprehend. Moreover, reference in the
appended claims to an apparatus or system or a component of an
apparatus or system being adapted to, arranged to, capable of,
configured to, enabled to, operable to, or operative to perform a
particular function encompasses that apparatus, system, or
component, whether or not it or that particular function is
activated, turned on, or unlocked, as long as that apparatus,
system, or component is so adapted, arranged, capable, configured,
enabled, operable, or operative.
All examples and conditional language recited herein are intended
for pedagogical objects to aid the reader in understanding the
invention and the concepts contributed by the inventor to
furthering the art, and are construed as being without limitation
to such specifically recited examples and conditions. Although
embodiments of the present inventions have been described in
detail, it should be understood that various changes,
substitutions, and alterations could be made hereto without
departing from the spirit and scope of the disclosure.
* * * * *